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In Australia, with 20 million people and about 4 million dogs, an estimated 100,000 people are bitten each year, with varying degrees of severity.

According to the national Delta Dog Safety Program, around 14,000 of these victims will require treatment in accident and emergency departments of the nation's public hospitals, and 60 per cent of the serious bites will involve children under 10.

We are all spot-on when we think that a dog bite can be nasty. But what most of us don't know is that a human bite can be even nastier, especially if you get bitten on the hand.

About 5 per cent of dogs will eventually bite a human, and 90 per cent of these biting dogs were known to their victim.

The dog population is growing about four times faster than the human population. Dog bite wounds account for about 1 per cent of all emergency room visits.

The victims are mostly aged between 2 and 19 years. The wound is usually a puncture, a tear, or an abrasion.

The teeth and jaw muscles of a dog can generate some 30 atmospheres of pressure — enough to punch a hole through light sheet metal.

In the USA, about half the population will suffer a bite wound at some time in their life — usually from a dog. The US stats are that bites from fellow humans come in third, behind bites from dogs (number 1) and cat bites (number 2).

These human bites usually happen as a part of open aggression, but they can occur accidentally in sports and sexual activity. About two-thirds of human bites happen to the hand and arm, about 15 per cent to the head and neck, and 15 per cent to the chest.

Probably the nastiest wound is the human bite to the clenched fist — known as the "fight bite". It's not as if the biter has much to do with it, as it usually happens as a result of a punch to the mouth with a clenched fist.

Now the hand has a magnificent combination of power and delicacy, and so, the anatomy of the hand is very complex. Teeth can perforate the joint capsule, lacerate nerves and tendons, and even break bones.

In many cases, apart from the blood, the wound doesn't look too bad — but there can be serious injuries under the surface.

Delays in seeking medical attention can lead to very nasty conditions like septic arthritis or osteomyelitis.

Back in the days before antibiotics, human bites were to be feared. If a person sought medical attention more than one hour after the bite, in one-third of cases the limb was amputated — because of infection that set in.

Antibiotics have changed this. But even so, a human bite wound is often not stitched up for several days, and only after daily checks show that the wound is healing nicely without infection will the doctors sew it shut.

And this leads to the explanation of why human bites are nastier than dog bites.

First, there are many different species of bacteria that live in the mouth, but there are many more in the human mouth, as compared to the dog mouth.

The average human carries some 42 species of bacteria in their mouth — and this can rise to 190, if they suffer a dental disease such as gingivitis or periodontitis. These bacteria in the human mouth include both aerobes (that like oxygen) and anaerobes (that don't like oxygen) in a 10:1 ratio.

But besides bacteria, a human bite has also been known to transmit viruses such as herpes and hepatitis, but not HIV, the virus that causes AIDS.

On average, a human bite wound will grow 5.4 species of bacteria, but the corresponding figure for a dog bite wound is 2.8.

Now the second factor as to why human bites are so nasty is that most human bites are not in the bulk of the flesh, but are close to the bone, and can infect the bone.

That's another reason why the bite of a human bite is worse than that of a dog.

And that's probably why you should never bite the hand that feeds you.